以下のプログラムは、2つのファイルをXORして、ワンタイムパッド暗号化を使用して出力ファイルを作成します。mlockall外部メモリソースからキーファイルを取得するときに、ハードドライブにキーファイルの痕跡が残らないようにするために使用しようとしました。
mlockallのマニュアルページから：
mlock() and mlockall() respectively lock part or all of the calling process's
virtual address space into RAM, preventing that memory from being paged to the
swap area.
それが機能しているかどうかを確認し、mlockall正しく使用したかどうかを確認するにはどうすればよいですか？
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/mman.h>
int main(int argc, char **argv)
{
struct stat statbuf;
struct stat keybuf;
char buffer [20];
int key;
int data;
int output;
int count;
char ans;
int * buf;
FILE * keyfile;
FILE * sourcefile;
FILE * destfile;
if(geteuid() !=0)
{
printf("Root access is required to run this program\n\n");
exit(0);
}
if(argc<4)
{
printf("OTP-Bunny 1.0\n");
printf("USAGE: OTP <source file> <output file> <keyfile>\n");
return (0);
}
/* Check number of arguments. */
if(argc>4)
{
printf("Too many arguments.\n");
printf("USAGE: OTP <source file> <output file> <keyfile>\n");
exit(1);
}
/* Allocate memory required by processes */
buf = (int*) malloc (sizeof(int));
if (buf == NULL)
{
perror("Error");
exit(1);
}
/* Lock down pages mapped to processes */
printf("Locking down processes\n");
if(mlockall (MCL_CURRENT | MCL_FUTURE) < 0)
{
perror("mlockall");
exit (1);
}
/* Check if sourcefile can be opened. */
if((sourcefile = fopen(argv[1], "rb"))== NULL)
{
printf("Can't open source file\n");
perror("Error");
printf("USAGE: OTP <source file> <output file> <keyfile>\n");
exit (1);
}
/* Get size of sourcefile */
fstat(fileno(sourcefile), &statbuf);
/* Check if keyfile can be opened. */
if((keyfile = fopen(argv[3], "rb"))== NULL)
{
printf("Can't open keyfile.\n");
perror("Error");
printf("USAGE: OTP <source file> <output file> <keyfile>\n");
exit(1);
}
/* Get size of keyfile */
fstat(fileno(keyfile), &keybuf);
/* Check if keyfile is the same size as, or bigger than the sourcefile */
if((keybuf.st_size) < (statbuf.st_size))
{
printf("Source file is larger than keyfile.\n");
printf("This significantly reduces cryptographic strength.\n");
printf("Do you wish to continue? (Y/N)\n");
fgets(buffer, 20, stdin);
sscanf(buffer, "%c", &ans);
if(ans == 'n' || ans == 'N')
{
exit (1);
}
if(ans == 'y' || ans == 'Y')
{
printf("Proceeding with Encryption/Decryption.\n");
}
else
{
printf("No option selected. Exiting...\n");
exit (1);
}
}
/* Check if destfile can be opened. */
if((destfile = fopen(argv[2], "wb"))== NULL)
{
printf("Can't open output file.\n");
perror("Error");
exit(1);
}
/* Encrypt/Decrypt and write to output file. */
while(count < (statbuf.st_size))
{
key=fgetc(keyfile);
data=fgetc(sourcefile);
output=(key^data);
fputc(output,destfile);
count++;
}
/* Close files. */
fclose(keyfile);
fclose(sourcefile);
fclose(destfile);
printf("Encryption/Decryption Complete.\n\n");
/* delete keyfile option. */
printf("Do you wish to delete the keyfile? (Y/N)\n");
fgets(buffer, 20, stdin);
sscanf(buffer, "%c", &ans);
if(ans == 'y' || ans == 'Y')
{
if ( remove(argv[3]) == 0)
{
printf("File deleted successfully.\n");
}
else
{
printf("Unable to delete the file.\n");
perror("Error");
exit(1);
}
}
/* cleanup */
printf("Releasing memory\n");
free (buf);
return(0);
}